Across
1
Second lightest element
4
Unit of power
6
Preserved remains of ancient life
8
Biological catalyst
9
Center of an atom or cell
Down
2
Substance with pH below 7
3
Measure of matter in an object
5
Hottest planet in solar system
7
Form of thermal energy
10
Chemical element in table salt
11
Curved glass that refracts light
12
Path of a planet around the sun
13
Basic unit of life